CPR compression device and method

ABSTRACT

Improved automatic chest compression systems which use constricting belts, repeatedly inflating bladders, or reciprocating pistons to compress the chest. A bladder is placed between the chest and the particular mechanism used to compress the chest during CPR. The bladder maximizes the effectiveness of chest compressions.

This application is a continuation of U.S. App. Ser. No. 10/192,771filed Jul. 10, 2002, now U.S. Pat. No. 6,939,314, which is acontinuation-in-part of co-pending application Ser. No. 09/866,377,filed May 25, 2001.

FIELD OF THE INVENTION

This invention relates to emergency medical devices and methods and theresuscitation of cardiac arrest patients.

BACKGROUND OF THE INVENTION

Current American Heart Association guidelines call for chestcompressions during cardio-pulmonary resuscitation (CPR) to be performedat a rate of 80 to 100 per minute and at a depth of 1.5 inches to 2.0inches. (Guidelines 2000 for Cardiopulmonary Resuscitation and EmergencyCardiovascular Care, 102 Circulation Supp. I (2000).) When a first aidprovider performs CPR according to these guidelines, blood flow in thebody is about 25 to 30% of normal. However, when chest compressions arerequired for long periods of time it is difficult, if not impossible, tomaintain adequate compression of the heart and rib cage. Evenexperienced paramedics cannot maintain adequate chest compressions formore than a few minutes. Hightower, et al., Decay In Quality Of ChestCompressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus,long periods of CPR, when required, are often not successful atsustaining or reviving the patient. At the same time, it appears that ifchest compressions could be adequately maintained then cardiac arrestvictims could be sustained for extended periods of time. Occasionalreports of extended CPR efforts (45 to 90 minutes) have been reported,with the victims eventually being saved by coronary bypass surgery. SeeTovar, et al., Successful Myocardial Revascularization and NeurologicRecovery, 22 Texas Heart J. 271 (1995).

In efforts to provide better blood flow and increase the effectivenessof resuscitation efforts, we have developed a chest compression systemwhich automatically compresses the chest of a heart attack victim. Thedevice includes a broad belt that wraps around the chest of the patient.The belt is repeatedly tightened around the chest to cause the chestcompressions necessary for CPR. Our devices are described in co-pendingapplication Ser. No. 09/866,377 filed May 21, 2001 and Ser. No.09/087,29 filed May 29, 1998, the entire disclosures of which are herebyincorporated by reference. Other modifications of the basic CPRprocedure have been proposed. Woudenberg, Cardiopulmonary Resuscitator,U.S. Pat. No. 4,664,098 (May 12, 1987) shows such a chest compressiondevice that is powered with an air cylinder. Waide, et al., ExternalCardiac Massage Device, U.S. Pat. No. 5,399,148 (Mar. 21, 1995) showsanother such device which is manually operated. Lach, et al.,Resuscitation Method and Apparatus, U.S. Pat. No. 4,770,164 (Sep. 13,1988), proposed compression of the chest with wide band and chocks oneither side of the back, applying a side-to-side clasping action on thechest to compress the chest. Kelly et al., Chest Compression Apparatusfor Cardiac Arrest, U.S. Pat. No. 5,738,637 (Apr. 14, 1998) uses aflexible, inelastic belt attached to a scissors-like means forcompressing the chest. Inflatable vests are also proposed forcompressing the chest for CPR, as shown in Halperin, CardiopulmonaryResuscitation and Assisted Circulation System, U.S. Pat. No. 4,928,674(May 29, 1990). The commercially available Thumper device, shown inBarkolow, Cardiopulmonary Resuscitator Massager Pad, U.S. Pat. No.4,570,615 (Feb. 18, 1986) and other such devices, provides continuousautomatic closed chest compression. Barkolow provides a piston which isplaced over the chest cavity and supported by an arrangement of beams.The piston is placed over the sternum of a patient and set to repeatedlypush downward on the chest under pneumatic power.

SUMMARY

The devices and methods described below provide for improved chestcompression in automatic chest compression systems which useconstricting belts, repeatedly inflating bladders, or reciprocatingpistons to compress the chest. A bladder is placed between the chest andthe particular mechanism used to compress the chest during CPR. Thebladder maximizes the effectiveness of chest compressions in a wideclass of patients. The bladder also helps to ensure that unequal orunnecessary pressure is not applied to the rest of the thorax, andevenly distributes the pressure applied by the belt, bladder, or pistonused for compression.

The bladder may be provided in several forms. The bladder may beconstructed with three or more laterally arranged chambers or sectionsin fluid communication with each other. The bladder may be filled with aresilient reticulated or open cell foam to provide structural resilienceto the bladder. An equalizing valve may be provided in the bladder toallow the pressure in the bladder to equalize with ambient atmosphericpressure. Otherwise, the bladder is substantially fluid-tight, and doesnot permit substantial flow of fluid into and out of the bladder duringcompressions, in contract to active bladders used in inflatable vestsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a patient receiving chest compressions from a chestcompression device in conjunction with a bladder.

FIG. 2 illustrates an exploded view of the bladder.

FIG. 3 illustrates a cross section of the bladder.

FIG. 4 illustrates the stiffness of a patient's thorax modeled as aseries of springs.

FIG. 5 is a cross section of a patient in an automatic chest compressiondevice and a bladder disposed over the sternum of the patient.

FIG. 6 is a cross section of a patient in an automatic chest compressiondevice during a compression and a bladder disposed over the sternum ofthe patient.

FIG. 7 illustrates a cross section of a bladder with the bottom surfaceof the central section made from an elastic material.

FIG. 8 illustrates a cross section of a bladder where the bottom surfaceof the central section is provided with pleats.

FIG. 9 illustrates a patient in an automatic chest compression device, afirst bladder disposed above the sternum, and a second bladder disposedabove the bladder.

FIG. 10 illustrates a patient in an automatic chest compression device,a first bladder disposed above the sternum, and a second bladderdisposed below the first bladder.

FIG. 11 illustrates a patient in an automatic chest compression device,a five-sectioned bladder disposed above the sternum, and a secondbladder disposed above the five-sectioned bladder.

FIG. 12 illustrates a patient receiving chest compressions from a chestcompression device in conjunction with a bladder.

FIG. 13 is a side view of the patient, bladder, actuator, piston, andcompression plate shown in FIG. 12.

FIG. 14 illustrates a barrel-chested patient receiving chestcompressions from a chest compression device in conjunction with abladder.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a patient 1 with a chest compression device 2 fittedon the patient and ready for use. A belt 3 and a belt tighteningmechanism within the backboard comprises the means for compressing thechest of the patient. The belt is operably connected to the belttightening mechanism, which provides the force necessary to tighten thebelt about the patient's chest and thorax. The belt tightening mechanismmay be a motor and motor driven spool as shown in co-pending applicationSer. No. 09/866,377, other automatic means for tightening the belt, or apull-lever or other manual means for tightening the belt.

A bladder 4 is disposed between the patients chest and the compressionbelt. The bladder 4, shown in phantom to indicate its position below thebelt, is secured to the belt 3. In turn, the belt is secured to the bodywith two overlapping areas 5 and 6 of hook and loop fastener, Velcro®,or other fastener. The bladder 4 may be provided with a sensing line 7which is connected to a pressure transducer or other means for measuringthe pressure in the bladder. The pressure transducer is in turnelectrically connected to a controller. The bladder itself may beprovided with the pressure transducer, in which case a signaltransmission cable 8 electrically connects the pressure transducer to acontroller. The controller, as illustrated in co-pending applicationSer. No. 09/866,377, uses the pressure in the bladder as feedback forcontrolling the force of compression and the amount of belt tighteningaccomplished by the belt tightening mechanism.

The central section 9 of the bladder 4 is disposed over the sternum ofthe patient. The right lateral section 10 is disposed over the rightlateral portion of the patient's chest and the left lateral section 11is disposed over the left lateral portion of the patient's chest. Theleft and right lateral sections of the bladder extend along themedial-lateral direction over the patient's rib cage. Depending on thelength of the bladder, the left lateral and right lateral sections maycompletely cover the patient's rib cage. For most patients, however, thebladder covers the anterior surface of the chest from armpit to armpitand along the superior-inferior length of the sternum. Thus, the entirebladder 4 may be about 6 to 8 inches high (as defined bysuperior-inferior axis 12), about 12 to 16 inches wide (as defined bymedial-lateral axis 13), and about 1.5 inches thick. When provided inthis size range, the bladder will cover substantially the entire chestof a typical patient. Specifically, a rectangular bladder of about 8inches high by about 16 inches wide (again, relative to the patient) byabout 1.5 inches thick is suitable to fit most patients, and may beprovided for use on all patients.

The bladder 4 is filled with a pressure-transmitting medium, such as agas or liquid. The bladder may also be filled with foam, such as anopen-cell foam or a filter foam, that allows air to flow throughout thebladder. The foam provides the bladder with structural support such thatthe bladder does not collapse if the bladder is not filled with apressure-transmitting medium. In addition, the bladder 4 may be providedwith a valve 20 that allows a user to either increase or decrease thepressure inside the bladder.

For most patients the sternum is easier to compress than the rest of thechest and thorax; thus, during compressions the bladder's right lateralsection 10 and left lateral section 11 are compressed more than thecentral section 9. In response, the fluid in the bladder is forced intothe bladder's central section. The central section will bulge inresponse to the pressure and the bulging results in preferentialdisplacement of the sternum. This effect occurs in both single-sectionedand multi-sectioned bladders.

In all patients, the bladder alters the pressure on the patient's chestduring compressions, creating a uniform field of pressure over theentire chest. The uniform pressure field has the effect of firstcompressing the chest in the most compliant regions of the chest.(Hence, in most patients the peri-sternal region is compressed first).In turn, the next most compliant part of the chest will be compressedsomewhat more than the next least compliant portion. Ultimately, theentire chest is compressed to at least some extent, with the mostcompliant regions of the chest being compressed more than the leastcompliant regions of the chest. Thus, during chest compressions, thepressure field maximizes the reduction in thoracic volume for a givenforce applied to the chest. Accordingly, the presence of the bladdercreates more effective blood circulation during chest compressions.

In addition, the bladder allows the chest compression device to applymore total force to the patient while also decreasing the probability ofhurting the patient, since the force per unit area on the chest isaltered by the presence of the bladder. A bladder allows the total forceapplied to the chest to be about 100 pounds to about 700 pounds. Wepreferably apply about 350 to 400 pounds of total force to the chestwith the chest compression belt illustrated in the Figures. Thus, thebladder allows a chest compression device to far exceed previously knowntotal force limits during chest compressions while maintaining ordecreasing the probability, as compared to manual compressions ordevice-driven compressions without a bladder, of injuring the patient.Conversely, because the bladder may have a bottom surface area of about100 square inches, the force density (the per square inch force applied)may be well below typical manual CPR levels, and effective CPRcompressions can be provided with forces of less than 10 psi applied onthe chest. We preferably apply about 2.50 to 4 pounds per square inch tochest with the chest compression belt illustrated in the Figures.

FIG. 2 illustrates an exploded view of the bladder 4, including a foaminsert 21. The bladder 4 is formed from two pieces of material melted,glued, or otherwise joined together along edges 22, 23, 24, and 25. Inaddition, the front side 26 and back side 33 of the bladder 4 are joinedor sealed together (mechanically or otherwise) at two dividers 27, alsoreferred to as dividing seams. Each divider 27 is about 1/16 inch toabout 1 inch wide (as defined by superior-inferior axis 12) and about ½inch to about the length of the bladder long (as defined bylateral-medial axis 13). Furthermore, creases 28 may be placed in thedividers so that the bladder 4 more easily folds. An equalizing checkvalve 29 is placed in line with an aperture 30 to provide forequalization of the bladder pressure with ambient atmospheric pressurewhen the device is not in use, while providing a tight seal duringcompressions, as more fully explained below.

Preferably, each divider 27 does not completely seal off the individualsections from each other (the dividers do not extend along the entiresuperior-inferior height of the bladder). Thus, fluid can communicatebetween the sections through fluid communication channels 31.Nevertheless, in alternate embodiments the dividers may completely sealone or more bladder sections from the other bladder sections. Inaddition, the dividers 27 are disposed away from the center of thebladder such that the center section may be wider along medial-lateralaxis 13 than the left lateral and right lateral sections. Thus, thecentral section is large enough to expand and effectively compress thesternum.

FIG. 3 illustrates a cross section of the bladder 4, showing the threebladder sections (the right lateral section 10, the left lateral section11, and the center section 9). The cross section is taken along line 32in FIG. 2 (which passes through the fluid communication channels 31).The front side 26 and the back side 33 of the bladder are not joined atthe fluid communication channels 31; thus, fluid may pass between thebladder sections. The bladder illustrated has been formed of a singlebladder with multiple chambers having fluid communication channelsconnecting the chambers. The bladder system may also be considered asseveral distinct bladders fastened together and connected by tubes whichprovide for the desired fluid communication between the bladders.

FIG. 4 illustrates the stiffness of a hypothetical patient's thorax 34modeled as a series of springs 35 of differing spring constants. Formost patients, the area corresponding to the sternum is most compliant(least stiff) and thus is labeled as having a spring constant 1K. Thelateral portions of the thorax are less compliant (more stiff) and thusare labeled as 2K or 3K. Since less force is needed to compress thesternal area of the thorax, energy efficiency is greatest whencompressing the sternum. This effect increases as the chest iscompressed further towards the spine. The addition of the bladder to thechest compression belt provides a compression device which takesadvantage of this model, as shown in FIGS. 5 and 6.

FIG. 5 is a cross section of a patient 1 in an automatic chestcompression device 2 with bladder 4 disposed over the sternum 40 of thepatient, between the chest of the patient and the belt. The device issimilar to that described in our parent patent application Ser. No.09/866,377. The bladder 4, having a central section 9, a right lateralsection 10, and left lateral section 11, is disposed over the patient'ssternum. The bladder helps apply force preferentially to the sternumwhile ensuring that other areas of the thorax receive an evendistribution of force during compressions.

The belt left section 41 and right sections 42 are joined in a seam topull straps 43. The pull straps are fixed to the drive spool 44. Thebelt right section 42 extends from the pull strap medial end 45 (thatis, the end near the medial area of the body, when applied to apatient), under the medially located lower spindle 46 and the lateralupper right spindle 47, under a spinal support platform 48 and furtheroutward to extend under the right flank of the patient when in use. Thebelt left section 41 extends from the pull strap medial end 45,reversing direction around the lateral upper left spindle 49, under thespinal support platform 48 and further outward to extend under the leftflank of the patient when in use. When not in use the belt is containedin belt housings 50. The spinal support platform 48 extends inferiorlyand superiorly over the cartridge and serves to support the patient overthe cartridge and away from the underlying area in which the belt runsinto the cartridge. Thus a large portion of the frictional load that thebelt would otherwise have to overcome during operation is eliminated. APTFE (Teflon®) sheet (not shown) may be provided on the upper surface ofthe spinal support platform to reduce friction and rubbing due to chestcompressions. Depending on the lateral spacing of the lateral spindles,the belt may engage the chest without engaging the side and back portionof the thorax, or it may engage substantially the entire circumferenceof the thorax. As shown, the lateral spindles are spaced so that thebelt engaged the chest and sides of the patient, but does not directlyengage the patient's back.

The operation of the spinal support platform 48 can also be seen inFIGS. 5 and 6. The platform extends laterally across the spinaldepression 51 that runs up and down the back. The width of the spinalsupport platform is chosen so that, in most patients, it extendslaterally to the shoulder blades (scapula) 52 or medial border of thescapula 53 of the patient, or to the protrusion of the trapezius muscle54 on either side of the spinal depression of the back 51. The platformthus spans the spinal depression 51, and extends bi-laterally across thespinal depression to the protrusions of the trapezius muscle 54 or themedial border of the shoulder blade 53. The belt sections 42 and 41 passunder the platform through a vertical gap between the platform and thecartridge or back plate, thereby avoiding running directly between thepatient's body and the cartridge for a small lateral width extendingslightly beyond the width of the platform. Also shown in FIGS. 5 and 6are the right lateral support plate 55 and left lateral support plate 56of the automatic chest compression device. The patient's thorax 34 andspine 57 are also shown for reference.

FIG. 6 is a cross section of a patient 1 disposed in an automatic chestcompression device 2 during a compression and a bladder 4 disposed overthe sternum 40 of the patient. During compressions the thorax 34 ismaintained in a somewhat oval cross section. However, since the lateralportions of the thorax are less compressible than the sternum, the forceof compressions forces fluid pressure from the left lateral section 11and right lateral section 10 to the center section during compressions.In response, the center section 9 deforms preferentially, causing thesternum to compress more than if there had been no bladder.

As seen in FIGS. 5 and 6, the bladder has a first relaxed configurationwhich it assumes when the belt is loosened about the chest, as in FIG.5, and a second pressurized configuration which it assumes when the beltis constricted about the chest of the patient, as in FIG. 6. In therelaxed configuration, the right lateral section, center section andleft lateral section are each filled with fluid. In the pressurizedconfiguration, the right lateral section and left lateral section aresubstantially compressed and some or all of the fluid therein is forcedinto the center section. (The bladder is substantially fluid-tight, anddoes not permit substantial flow of fluid into and out of the bladderduring compressions.) The relative sizes of the bladder sections may beadjusted (by appropriate location of the seams that join the upper andlower sheets) to provide chambers of appropriate relative size so thatthe lateral chambers are not fully compressed and emptied of fluid whencompressed with the forces expected during compressions, and theanterior-posterior bulging of the central section is limited. (In thecase of a single sectioned bladder the sternum will still bepreferentially compressed. The edges of the single-section bladder willstill be squeezed, forcing fluid into the central portion of thebladder. Thus, the central portion of the single sectioned bladderexpands and causes the thorax to compress preferentially.)

FIG. 7 illustrates a cross section of a bladder 4 with the bottomsurface 66 of the central section made from an elastic material, such aslatex. Alternatively, the bladder bottom surface 66 can be neoprene,rubber, rubber-coated lycra, or some other elastic material. Althoughonly the bottom portion of the central section 9 is made from an elasticmaterial, the entire central section can also be made from an elasticmaterial. In contrast, the right lateral section 10 and left lateralsection 11 are made from a relatively inelastic material. In the case ofa single-sectioned bladder, a portion of the bottom surface may be madefrom an elastic material.

When the bladder comes under the expected load from a compression belt,the fluid in the lateral sections 10 and 11 will move into the centralsection 9. Since the bottom surface 66 of the central section isflexible, the central section 9 will expand more than when the centralsection does not have an elastic bottom surface. In the case of a singlesectioned bladder, the lateral portions of the bladder will force fluidinto the central portion of the bladder, causing the elastic portion toexpand preferentially. The central portion of the bladder expands in theposterior direction relative to the patient, distributing the forceapplied by the belt evenly over compliant and non-compliant portions ofthe chest. In the typical patient, the sternum is displaced posteriorlywith this device.

FIG. 8 illustrates a cross section of a bladder 4 where the bottomsurface 66 of the central section 9 is provided with pleats or folds,which are oriented up and down relative to the body of the patient. Theentire bladder is made from a relatively inelastic material, though thepleated section could be made from an elastic material. Alternatively,the entire central section 9 could be made such that both the top andbottom surfaces are pleated. In either case, the number of pleats orfolds in the pleated bottom surface shown is within the range of 1 toabout 10 pleats (2 to about 20 bends), though about 5 pleats (10 bends)is used for most patients. In the case of a single-sectioned bladder, aportion of the bottom surface may be pleated.

When the bladder experiences a load the lateral sections 10 and 11 willtransfer pressure to the central section 9. Since the bottom surface 66of the central section is pleated it will expand preferentially. In thecase of a single sectioned bladder, the lateral sections of the bladderwill force fluid into the central sections of the bladder, causing thepleated portion to expand preferentially. Since the central portion ofthe bladder expands preferentially, the sternum also compressespreferentially.

FIG. 9 illustrates a patient 1 in an automatic chest compression device2, a first bladder 4 disposed above the sternum, and a second bladder 67disposed above the first bladder. (The second bladder may also be a pad,a single section of foam, or a multi-sectioned bladder). The belt inthis Figure is spooled upon a centrally located drive spool 44, whichspools the belt as it is drawn over the laterally located spindles 47and 49. The spindles are laterally spaced wider than the patient'sthorax 34, so that the belt extends over the chest without substantiallyengaging the remainder of the thorax. The belt 3, or other means forcompressing the chest, secures both bladders to the patient's chest (theanterior surface of the thorax 34). The second bladder 67 is constructedwith a relatively inelastic material such that its shape changes onlyslightly with changes in pressure. The second bladder may be filled witha pressure-transmitting medium such as air, gel, hydro-gel, foam, water,or other suitable fluids.

The second bladder 67 alleviates local areas of high pressure on thepatient's thorax 34. In other words, in areas other than over thesternum, the pressure will remain evenly distributed. Duringcompressions, the second bladder also helps to transfer pressure fromthe lateral sections 68 of the second bladder to the central section 9of the bladder by pressing on the lateral sections 10 and 11 of thebladder 4.

FIG. 10 illustrates a patient 1 in an automatic chest compression device2, a first bladder 4 disposed above the sternum 40, and a second bladder67 disposed below the bladder. In this orientation, the second bladderhelps to more evenly distribute the force of compressions along thepatient's thorax 34, although preferential displacement of the sternummay still take place during compressions.

FIG. 11 illustrates a patient 1 in an automatic chest compression device2, a five-sectioned bladder 69 disposed above the sternum 40, and asecond bladder 67 disposed above the five-sectioned bladder. Thefive-sectioned bladder allows fluid communication between the leftlateral section 70, left medial section 71, right lateral section 72,right medial section 73, and the central section 9. Thus, when under aload the fluid pressure will transfer from the lateral and medialsections to the central section. This results in preferentialdisplacement of the sternum 40 as the central section 9 preferentiallyexpands.

The five-sectioned bladder 69 is made of similar materials and filledwith similar liquids or foams as the bladder 4. In addition, the centralsection 9 of the five sectioned bladder may be constructed with eitheran elastic or a pleated bottom surface 66. In general, a bladder mayhave any number of sections. However, for most applications a bladderwith three sections fits the patient well and also preferentiallycompresses the patient's sternum during compressions.

FIG. 12 illustrates a patient 1 receiving chest compressions from achest compression device in conjunction with a bladder 4. An actuator 81(or other means for providing force) drives a piston 82, and the pistondrives a compression plate 83 towards a back plate 84 or other rigidsurface. The compression plate compresses the chest as it is repeatedlyforced downward on the chest. The plate is sized and dimensioned tocover substantially the entire anterior surface of the chest. A bladder4 is disposed between the compression plate 83 and the patient's chest.The bladder shown in FIG. 12 is single-sectioned (but may bemulti-sectioned) and is filled with a pressure-transmitting medium.

As the compression plate is driven towards the patient's chest, thebladder 4 deforms. Because the sternum 40 is easier to compress than thelateral and medial portions of the patient's chest, the bladder'slateral portions, 10 and 11, are compressed more than the bladder'scentral portion 9. Thus, pressure is transmitted to the central section9, which in turn causes the central portion of the bladder to expand.The expansion of the central portion of the bladder causes the chest tobe compressed posteriorly in the location of the sternum 40. This effectoccurs in both single-sectioned and multi-sectioned bladders.

FIG. 13 is a side view of the patient 1, bladder 4, actuator 81, piston82, and compression plate 83 shown in FIG. 12. The bladder may be sizedand proportioned to occupy the entire area of the bottom of thecompression plate 83. The bladder may be smaller, though the bladder isstill large enough to cause preferential displacement of the sternum 40as the bladder deforms during compressions.

FIG. 14 illustrates the effect of the compression device on abarrel-chested patient 85. The chest compression device performscompressions by repeatedly tightening and loosening a belt 3 disposedover the patient's chest, and is shown in FIG. 14 in its compressionstate. The bladder 4 is disposed between the belt 3 and the patient'ssternum 40. In most patients, the bladder will cause the patient'ssternum to be compressed preferentially. However, with barrel-chestedpatients, the sternum is less compliant, and offers more resistance tocompression than the sternum of the typical patient. When the chestcompression device is applied and operated on a barrel-chested patient,the bladder's right lateral section 10, left lateral section 11, andcentral section 9 tend to compress more evenly, as shown in FIG. 14.Nevertheless, CPR remains effective and the bladder continues tore-distribute the pressure of compressions. Thus, more total force canbe applied to the patient's chest without significantly increasing therisk of injury to the patient.

A variety of other CPR devices may also be used in conjunction with thebladder. A belt or band may be disposed around the patient's chest andvarious other means for tightening the belt (such as a manualpull-lever, scissors-like device, or motor) be operably attached to thebelt. The device shown in the Kelly (U.S. Pat. No. 5,738,637), forinstance, includes a base adapted for placement over the central regionof a patient's chest, coupled to an actuator which is connected to abelt configured to wrap around the patient's chest and a “forceconverter” mounted on the base and coupled to the actuator and the belt.The force converter converts forces applied downwardly on the actuatorinto tangential forces applied to the belt. The bladder described abovecan be interposed between the base described in Kelly to further refinethe application of force to the patient.

In other devices the means for compressing the chest may comprise apiston, a plate, or other means for applying force to the chest operablyconnected to a means for driving the piston, plate, or other means forapplying force, such as the Thumper™ device. The means for driving thepiston, plate, or other means for applying force may comprise a motor,manual pull-lever, an actuator, or other means for driving a means forapplying force to the patient's chest. The bladder may also be used inconjunction with manual chest compressions when compressions areperformed with a rigid compression surface, such as a compression board.In any case, the bladder may be provided between the compressing deviceand the patient's chest and, in use, performs similarly to the devicesshown in FIGS. 1, 5 and 6. In another device the bladder may be disposedbetween a compression vest and the patient's chest. The bladder may beused with any chest compression technique that uses a means for applyinga force to the chest of the patient.

The bladder may also comprise many forms. The bladder 4 may be singlesectioned or may be multi-sectioned. The bladder 4 may be of varioussizes with a volume of up to several hundred cubic centimeters. Theentire bladder 4 may be about 3 to about 18 inches high (relative to thepatient, as defined by superior-inferior axis 12), about 4 to about 24inches wide (relative to the patient, as defined by lateral-medial axis13), and about ¼ inch to about 3 inches thick. The bladder 4 may assumea variety of shapes in addition to the rectangular bladder shown,including a cylinder, or other geometrical shape having a thicknesssmaller than the bladder's width and length. Thus, the bladder may beprovided in a variety of sizes to match the chest size of differentpatients, such as men, women, very small individuals, or very largeindividuals.

The bladder 4 may comprise an inelastic material such as double-coatedurethane over a high strength fabric, including polyester, Kevlar®, or a200 Denier Nylon Oxford fabric. Other materials of similar strength andinelasticity may be used, and the bladder may be formed of separatepieces as shown in FIG. 2, or it may be formed by injection molding orother processes. The material may be slightly elastic, and may stretchabout 20% when in use. The modulus of the material may be greater thanabout 2000 psi. However, the bladder itself is designed such that thecentral bladder section 9 expands when the lateral sections 10, and 11,are compressed. The bladder may be only partially filled with foam, foamcombined with air, or some other pressure-transmitting medium. In thiscase, the central section may still expand when the lateral sections arecompressed. Though the lateral sections may beneficially be compressedand deformed to the extent that they are completely emptied duringcompressions, the central section should not be so elastic or deformablethat it is completely flattened (so that the upper and lower sheetsmeet) during compressions.

Suitable foams for use with the bladder include SIF® foam, polyurethane,polyethylene, or other polymer foams. The foam may be from about 5 poresper inch to greater than 100 pores per inch, though about 15 pores perinch is sufficient for most applications. The bladder 4 may filled withair, foam, water, gel, hydrogel, alcohol, oil or any other fluid thatcan communicate pressure from the right lateral section 10 and the leftlateral section 11 to the central section 9 of the bladder. If filledwith a liquid, the liquid may have a low viscosity to allow for easiertransfer of the liquid between bladder sections. The liquid may also belight (of a low molecular weight) to lower the weight of the bladder.The bladder may also be provided with ribs made from plastic, or otherflexible material, to provide the bladder with a skeletal frame. Theskeletal frame may be used alone or in combination with the foam toenhance the resilient expansion of the bladder during relaxation of thechest compression device.

The bladder may be coated, on either the inner surfaces, outer surfaces,or both, to make it water resistant, water proof, or to make it easierto join sections of the bladder together (when forming multi-sectionedbladders). Whatever the material or coating, the bladder should beresistant to water and bodily fluids and maintain its materialproperties both wet and dry. Desirable coatings include polyurethane,polyester coated with polyurethane, polyether polyurethane, or similarmaterials. The thickness of the coating may vary, but is about 0.003inches to about 0.050 inches; however, a thickness of about 0.006 inchesis suitable for most bladder products.

The bladder may be provided with additional features if desired. Forexample, the bladder may be provided with markings or compartments toassist the rescuer in placing the bladder properly on the patient'schest. The bladder may be provided with a transducer, pressure sensor,or force sensor. The sensor may measure the force applied to the bladderor the pressure inside the bladder.

As mentioned above, the bladder may be provided with a valve whichpermits air to flow in and out of the bladder only when atmosphericpressure is about equal to the pressure in the bladder. In general, thevalve leaks when there is a small differential pressure across thevalve. That is, when the bladder pressure slightly exceeds ambientpressure the valve will allow pressure equalization. However, when thebladder pressure rises sharply (during compressions) the valvecompetently closes to prevent flow past the valve and out of thebladder. Thus, the valve performs as a leaky check valve that permitsleakage when there is a small differential pressure across the valve butseals tightly when there is a large differential pressure across thevalve. We refer to such valves as equalizing check valves.

The valve allows the bladder to be stored in an uninflated state (suchas when it is folded for packaging or transport) and yet achieveatmospheric pressure before the bladder is readied for use, and itallows the bladder to be manufactured and filled in one place andshipped to its location of use without taking any action to adjust thepressure in the bladder. Additionally, the valve permits consistentoperation of the device in scenarios in which ambient pressure maychange rapidly, such as during helicopter transport, use on aircraft, oruse in mountainous areas.

The valve may comprise any suitable valve that allows air to flow onlywhen atmospheric pressure is about equal to the pressure in the bladder.A simple example would be a floppy latex tube inside of the bladder influid communication with an aperture in the bladder opening to theoutside. In more complicated constructions, the valve may comprise a toplayer and a bottom layer, where at least the bottom layer is made of aresilient material. The top layer and bottom layer are sealed togetherwhile leaving least one relief conduit provided between the layers and ahole provided in the top layer. The top layer is disposed so that thehole opens to the atmosphere and the bottom layer is disposed so thatthe conduit opens inside the bladder. When atmospheric pressure is aboutequal to the pressure in the bladder then air flows back and forththrough the hole, through the relief conduits, and through the bladder.When pressure is applied to the bladder, the pressure in the bladderforces the layers together, causing the relief conduit to collapse andthus seal the bladder. A suitable valve of this type is described inPekar, Inlet Check Valve for Pump Mechanism, U.S. Pat. No. 5,372,487.

Another suitable valve is a membrane valve, wherein each membrane has asmall hole that lines up with the other small hole unless the valveexperiences a large increase in pressure. When a compression begins theholes no longer line up, thus sealing the bladder for the duration ofthe compression. Other means for maintaining the total amount of airwithin the bladder while the bladder is compressed is a peel-off tabthat is used to seal the bladder just before compressions, a classiccheck valve which is lightly spring biased to remain open, a check valvethat plugs during the first compression, or a ball check valve with aball in a tube that seals with the closure of a belt used to compressthe chest. Other valve examples include a plunger held down by Velcro™(or other releasably attached securing means) or other valves that closeat the beginning of compressions.

The bladder may be provided with other features, including a liner or acover that covers and protects the bladder and allows the bladder to bere-used. The liner may be designed for use as part of a belt or othercompression means, or the liner may merely cover the bladder withoutadditional features. (Thus, the pad and liner may be easily attached toa means for compressing the chest). The liner may comprise a lowfriction, water-resistant, non-resilient material such as PTFE, ePTFE(both are Teflon®), or similar materials. The liner may cover one ormore surfaces of the bladder, part of a bladder surface, or the entirebladder. In addition, one or more surfaces of the bladder may be coatedwith or made of PTFE, ePTFE (both are Teflon®), or similar materials.

The bladder may also be provided with an integrated defibrillationdevice, with ECG and defibrillation electrodes, and/or other electrodesto measure impedance. The ECG and defibrillation electrodes (which maybe the same electrodes as the impedance measurement electrodes) may bebreak-away electrodes that break off the surface of the pad when the padis removed from the patient. The electrodes then remain on the patient'schest for continued use in monitoring the patient. The bladder may alsobe provided with one or more means for measuring biological feedbackparameters of interest to medical personnel, including blood pressuremonitors, patient temperature, blood oxygen levels, or other biologicalparameters. In addition, the bladder may be designed to be usedrepeatedly on different patients, or may be designed to be disposablewith each rescue.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the inventions. Otherembodiments and configurations may be devised without departing from thespirit of the inventions and the scope of the appended claims.

1. A system for performing CPR on a patient, said system comprising: achest compression means comprising a belt adapted to be disposed atleast partially about the chest of the patient and a means forrepetitively tightening the belt at a resuscitative rate, said meansoperably connected to the belt; a bladder disposed between the chestcompression means and the chest of the patient, wherein the bladder isdivided to form a left lateral section in fluid communication with acentral section in fluid communication with a right lateral section, andwherein each section contains a pressure-transmitting medium, and thebladder is disposed relative to the belt during use such between thebelt and the chest of the patient and the central section is disposedover the sternum of the patient.
 2. The system of claim 1 wherein thepressure-transmitting medium comprises an open-celled foam.
 3. Thesystem of claim 2 further comprising a defibrillator operably connectedto the patient.
 4. The system of claim 2 further comprising a means formeasuring biological parameters operably connected to the patient. 5.The system of claim 2 wherein the bladder further comprises an aperturecommunicating from the interior of the bladder to the exterior of thebladder, and a valve controlling the aperture, wherein the valve is openwhen atmospheric pressure is about equal to the pressure inside thebladder and wherein the valve closes during a compression.
 6. The systemof claim 2 further comprising: a defibrillator operably connected to thepatient; a means for measuring biological parameters operably connectedto the patient; an aperture in the bladder, and a valve controlling flowthrough the aperture, wherein the valve is open when atmosphericpressure is about equal to the pressure inside the bladder and whereinthe valve closes during a compression.
 7. The bladder of claim 1 whereinthe bottom surface of the central section is made of an elasticmaterial.
 8. The bladder of claim 5 wherein the bottom surface of thecentral section is made of an elastic material.
 9. The bladder of claim6 wherein the bottom surface of the central section is made of anelastic material.
 10. The bladder of claim 1 wherein the bottom surfaceof the central section is pleated.
 11. The bladder of claim 10 whereinthe bottom surface of the central section is comprised of an elasticmaterial.
 12. A device for compressing the chest of a patientcomprising: a base adapted for placement over the central region of apatient's chest; an actuator connected to a belt configured to wraparound the patient's chest; a force converter mounted on the base andcoupled to the actuator and the belt, said force converter operable toconvert forces applied downwardly on the actuator into tangential forcesapplied to the belt; and a fluid-filled bladder disposed between thebase and the patient's chest the bladder being divided to form a leftlateral section in fluid communication with an expandable centralsection in fluid communication with a right lateral section.
 13. Thedevice of claim 12 wherein the bladder comprises: a right lateralsection adapted to be disposed over the right side of the patient'schest, a center section adapted to be disposed over the center of thepatient's chest, and a left lateral section adapted to be disposed overthe left side of the patients chest, and the bladder having a firstrelaxed configuration which it assumes when the belt is loosened aboutthe chest and a second pressurized configuration which it assumes whenthe belt is constricted about the chest of the patient; wherein in saidrelaxed configuration the right lateral section, center section and leftlateral section are each filled with fluid and in said pressurizedconfiguration the right lateral section and left lateral section aresubstantially compressed and the fluid therein is forced into the centersection.
 14. The device of claim 12, wherein the bladder furthercomprises: a resilient foam substantially filling the bladder.
 15. Thedevice of claim 13, wherein the bladder further comprises: a resilientfoam substantially filling the bladder.
 16. The device of claim 12,wherein the bladder spans substantially the entire breadth of thepatient's chest.
 17. The device of claim 12, wherein the bladder spanssubstantially the entire breadth and height of the patient's chest. 18.The device of claim 12, wherein the bladder is about 16 inches wide and8 inches high, relative to the patient.
 19. The device of claim 13,wherein the bladder spans substantially the entire breadth of thepatient's chest.
 20. The device of claim 13, wherein the bladder spanssubstantially the entire breadth and height of the patient's chest. 21.The device of claim 13, wherein the bladder is about 16 inches wide and8 inches high, relative to the patient.
 22. The device of claim 1,wherein the bladder further comprises a first fluid pathway connectingthe left lateral section and the central section and a second fluidpathway connecting the right lateral section and the central section.